1. Field of the Invention
The present invention relates to a process for formation of ceramic coatings on silver and/or silver plated articles in order to prevent surface tarnish of the articles, which are usually applied to accessories or ornaments of bags and garments.
2. Related Prior Art
Metal finishing technologies have progressed to enhance the utility of metals and focus on efforts to protect metals from corrosion, improve appearance and decorative value of metal articles and expand the functions of metal.
Metal finishing methods which have been previously developed include: an electroplating or electro-deposition method to form a metal coating over another metal or non-metal material by electrical energy, in which an electrolyte plated subject is an anode while a plating metal is a cathode; a chemical plating method to form a metal coating on the surface of another metal or non-metal by chemical modification, which has no electrode and comprises substitution of metal ions to be plated; a dip-plating method to form a coating by dipping a metal subject into a molten metal bath containing the plating metal; a penetration plating method to form an alloy coating by diffusing and penetrating a metal into another metal; a metal spraying method to form a coating by spraying a molten metal over the surface of another metal; a chemical deposition method to coat metal compounds by evaporating volatile metal salt and thermally decomposing the surface of a subject to be plated; a cathode sputtering method to form a coating on the surface of a subject to be plated with granular cathode material by colliding the cathode material with cation particles under a vacuum condition; a vacuum vapor deposition plating method to form a coating by depositing metal ions on the surface of a metal or non-metal object under a vacuum condition; an ion plating method to form a coating on a cathode material by converting a metal or gas through glow discharging into cations and accelerating the cations; an anodizing treatment method to form a thicker surface oxidized coating for an oxidation potential metal, which comprises immersing a material to form the oxidation coating in a water soluble solution containing sulfuric acid, chromium oxalate, etc. to accelerate oxidation thereof; a chemical coating treatment method to form a coating composed of chromates, phosphates or the like on the surface of a metal, which is different from the anodizing treatment because of using the oxidized coating made of a different metal from the plated object; a painting method to apply paint to the surface of a metal; a lining method to cover the surface of a metal or non-metal substrate with any non-metal material such as rubber or a synthetic resin; a coating method to form a coating made of enamel (that is, ceramic), synthetic resin, etc.; and a surface hardening treatment method to increase the hardness of the surface of a metal by penetrating carbon or nitrogen into the surface of the metal. However, metal finishing methods are not limited to only these particular kinds.
As described above, a variety of surface treatment methods have been known in the related art. However, there have not yet been proposed improved and/or easily applicable metal plating methods that endow silver or silver-plated articles with improved surface hardness of more than 500 Rv according to the Micro Vickers hardness test while indefinitely retaining the original silver color and gloss, and that form a coating film made of a metal with excellent corrosion resistance.
Conventionally known chemical coating methods for improving the specific strength of a coating film cannot form transparent coatings. In addition, none of the various chemicals previously developed can with certainty allow fabrication of electroplated products using metals with transparency, high specific strength and excellent corrosion resistance.
In the case of a method for electroplating silver or silver-plated articles by dipping the articles in an electrolyte, it is difficult to manage an acid bath or alkali bath containing the electrolyte. In this field, there has been proposed an electro-deposition process, which is the most well known method, that dips a metal subject in an aqueous lacquer and dries the wetted subject, or that applies an oil-based lacquer to a metal subject and carries out thermosetting of the coated subject. Such electro-deposition processes are generally used for surface coating of automobile structures.
However, unlike in the case of silver, this process does not regard maintenance of original color and gloss of a base paint as an important goal, and can control the gloss using a lacquer. Accordingly, the electro-deposition process is expected to be adapted simply because of economic merit.
It is often observed that silver-plated ornaments attached to even a high quality bag, which was purchased merely a few months earlier, are visibly tarnished, or a bright silver based trophy is discolored in a little while in spite of being carefully stored in a glass box. Especially, when leather-made bags with silver or silver-plated ornaments are placed in an export container for transportation, discoloration or tarnish of the ornaments may sometimes be caused by chemical ingredients contained in the leather and/or temperature variation during the transportation before arriving at consumers, thereby causing a problem of damage to the value of goods.
Discoloration or tarnish of a silver or silver-plated article is mostly caused by chemical modification such as corrosive oxidation of the surface of the article. Silver generally forms a plurality of silver oxides including, for example, AgCl, Ag2S, Ag2O and so on, and this means silver is a very susceptible metal to oxidation. In other words, silver is a lower level noble metal than other precious metals such as platinum, rhodium, palladium, gold and the like. Accordingly, this problem must be overcome in order to maximize the value of silver and silver plated articles.